1. Field of the Invention
This invention relates to a disposable diaper for infants, adults or incontinent persons, and particularly to a shorts type disposable diaper.
2. Description of the Prior Art
In general, disposable diapers include a vertically long body comprising a liquid permeable topsheet, a liquid impermeable backsheet, and an absorbent member interposed therebetween, the body being divided into a stomach portion which, when in wear, is located on the stomach side of its user and a back portion which, when in wear, is located on his back side.
As a known disposable diaper of this type, there is, for example, a flat type in which both side edges (side flaps) of the back portion are provided with fastening devices which, when in use, are fastened to the stomach portion of the body (Japanese Patent Publication No. Sho 52-40267).
There have been there was proposed a shorts type disposable diaper in which a pair of right and left side flaps formed along both longitudinal sides of the diaper body are connected and fixed together at both stomach and back portions to form a pair of right and left leg opening portions and a unitary waist opening portion (Japanese Patent Early Laid-open Publication No. Sho 61-207605). In the shorts type disposable diaper, both the pair of leg opening portions and the unitary waist opening portion are designed to be expansible so as to fit to the wearer's body. Usually, since the wearer can wear this shorts type disposable diaper in an upright position, it is used as a toilet training underwear for a baby to enable him to be free from a diaper as soon as possible. It is also usable for an incontinent person, or an adult who can walk.
The shorts type disposable diaper of this type has such feature, when compared with the so-called flat type diaper, as that the wearer can pull it up and down by himself just like normal underwear. In order to satisfy the requirement that the wearer himself can easily wear the diaper without leakage of waste,materials, the shorts type disposable diaper is required to have an excellent fitness. Moreover, the diaper is required to have a favorable compliance to the wearer's busy action.
In order to meet with such requirements as mentioned above, Japanese Patent Early Laid-open Publication No. Hei 2-4364 discloses a constitution, wherein an expansible side panel (side member) is provided to side portions for connecting a stomach portion with a back portion of a body, and elastic members are provided to an end portion of the stomach side and an end portion of the back side of the body.
That is, as is shown in FIG. 8, in a body 55 of a conventional diaper 51, an under-crotch portion is provided at both side edges thereof with side flaps 59a, 59b extending outward of an absorbent member 54, and the body 55 is provided at both end portions thereof with waist flaps 57a, 57b extending outward of the absorbent member 54, the side flaps 59a, 59b of the under-crotch portion being provided with elastic members 61, 61 which are arranged thereon in expansible states. Similarly, the waist flaps 57a, 57b are provided with elastic members 58a, 58b which are arranged thereon in expansible states in order to enhance the fitness around the wearer's waist. The body 55 is provided on both sides of its back portion with side panels 62, 62 and on both sides of its stomach portion with side panels 63, 63. Each of the side panels 62 and 63 are formed of an elastic member which is a separate member from the body 55, and the side panels 62 and 63 are connectable with each other at end portions 64, 64 thereof.
However, owing to the correlation of expanding lines of stress (indicated by two-headed arrows with empty inside in FIG. 9 at the leg opening portions and at the waist opening portion, which respectively are formed by the elastic members 61, 58a, 58b and the side panels 62, 63 having elasticity, as shown in its worn state in FIG. 9, the conventional shorts type disposable diaper 51 has the following problems.
The expression "expanding lines of stress" refers to expansible portions applied with gatherings formed of an elastic member.
That is, although the expanding lines of stress of the respective opening portions intersect with each other when they are extended, a gap portion X is sometimes formed between adjacent expanding lines of stress, the gap portion X where no expanding line of stress exists. For example, when the wearer is in a bending attitude, gaps X are formed between the diaper and the wearer at his stomach portion, and these gaps X are to be a cause of leakage.
Further, it has such problems as that since the side panels 62, 63 are formed of a separate member from the body, the number of component parts of the diaper is increased and the manufacturing process becomes complicated, thus resulting in high cost.
Furthermore, the side panels 62, 63 are of a unitary member, and the physical property of each portion is the same. Accordingly, in order to increase the fastening force for preventing a slip-down and enhancing the fitness, the expansion of the whole side panels 62, 63 is required to be increased. However, if the expansion is increased, an excessive oppressive sensation is given to the wearer or the increased expansion jeopardizes the wearer's smooth pulling-on and pulling-off performance.